Wideband laser-induced plasma filament antenna with modulated conductivity

Abstract

An antenna comprising: a radio frequency (RF) coupler; a transceiver communicatively coupled to the RF coupler; a laser configured to generate a plurality of femtosecond laser pulses so as to create, without the use of high voltage electrodes, a laser-induced plasma filament (LIPF) in atmospheric air, wherein the laser is operatively coupled to the RF coupler such that RF energy is transferred between the LIPF and the RF coupler; and wherein the laser is configured to modulate a characteristic of the laser pulses at a rate within the range of 1 Hz to 1 GHz so as to modulate a conduction efficiency of the LIPF thereby creating a variable impedance LIPF antenna.

We claim: 
     
       1. A method for modulating a laser-induced plasma filament (LIPF) antenna comprising the steps of:
 using a laser to generate a LIPF within an optically-transparent medium, wherein the laser is configured with an energy of at least 100 mJ and a pulse duration no longer than 20 ns; 
 communicatively coupling the LIPF to a transceiver; and 
 modulating a conduction efficiency of the LIPF by adjusting the LIPF's localized energy density at a rate within the range of 1 Hz to 1 GHz by altering an optical focal length of the laser thereby creating a variable impedance LIPF antenna. 
 
     
     
       2. The method of  claim 1 , further comprising the step of altering the focus of the laser until a change in an index of refraction of the optically-transparent medium results in a plasma cloud formation at a distal end of the LIPF thereby creating an antenna with a high instantaneous bandwidth. 
     
     
       3. A method for modulating a laser-induced plasma filament (LIPF) antenna comprising the steps of:
 using a laser to generate a LIPF within an optically-transparent medium, wherein the laser is configured with an energy of at least 100 mJ and a pulse duration no longer than 20 ns; 
 communicatively coupling the LIPF to a transceiver; 
 modulating a conduction efficiency of the LIPF by adjusting the LIPF's localized energy density at a rate within the range of 1 Hz to 1 GHz thereby creating a variable impedance LIPF antenna; and 
 adjusting the power of the laser until a desired conductivity of the LIPF at a distal end of the LIPF is achieved thereby creating an antenna with a high instantaneous bandwidth. 
 
     
     
       4. The method of  claim 1 , wherein the pulse duration of the laser is between 30-100 femtoseconds thereby creating a LIPF having a lifetime in the range of 1-10 nanoseconds. 
     
     
       5. The method of  claim 1 , wherein the pulse duration of the laser is between 100 attoseconds and 100 nanoseconds, and wherein the time between pulses is adjustable, thereby creating a LIPF having a lifetime in the range of 1 nanosecond to 1 second. 
     
     
       6. A method for modulating a laser-induced plasma filament (LIPF) antenna comprising the steps of:
 using a laser to generate a LIPF within an optically-transparent medium, wherein the laser is configured with an energy of at least 100 mJ and a pulse duration no longer than 20 ns; 
 communicatively coupling the LIPF to a transceiver; 
 modulating a conduction efficiency of the LIPF by adjusting the LIPF's localized energy density at a rate within the range of 1 Hz to 1 GHz thereby creating a variable impedance LIPF antenna; and 
 using the variable impedance LIPF antenna as a reflector to reconfigure a neighboring metallic antenna such that a performance characteristic of the neighboring metallic antenna is altered. 
 
     
     
       7. The method of  claim 6 , wherein the altered performance characteristic is selected from the group consisting of: frequency, gain profile and directivity. 
     
     
       8. The method of  claim 1 , wherein the optically-transparent medium is a gas. 
     
     
       9. An antenna comprising:
 a first radio frequency (RF) coupler; 
 a transceiver communicatively coupled to the first RF coupler; 
 a first laser configured to generate a plurality of femtosecond laser pulses so as to create, without the use of high voltage electrodes, a first laser-induced plasma filament (LIPF) in atmospheric air, wherein the first laser is operatively coupled to the first RF coupler such that RF energy is transferred between the first LIPF and the first RF coupler; 
 wherein the first laser is configured to modulate a characteristic of the laser pulses at a rate within the range of 1 Hz to 1 GHz so as to modulate a conduction efficiency of the first LIPF thereby creating a variable impedance LIPF antenna; 
 a second RF coupler communicatively coupled to the transceiver; and 
 a second laser configured to generate a plurality of femtosecond laser pulses so as to create, without the use of high voltage electrodes, a second LIPF in atmospheric air, wherein the second laser is operatively coupled to the second RF coupler such that RF energy is transferred between the second LIPF and the second RF coupler and wherein the second LIPF is disposed with respect to the first LIPF such that together the first and second LIPFs form a dipole antenna. 
 
     
     
       10. The antenna of  claim 9 , further comprising a third laser configured to generate a reflector LIPF that has a length that is longer than the dipole antenna, and further configured to generate a plurality of LIPF directors that are parallel to, and shorter in length than, the dipole antenna and are positioned on an opposite side of the dipole antenna from the reflector LIPF such that the LIFP directors absorb and reradiate radio waves from the dipole antenna with a different phase, modifying the dipole antenna's radiation pattern. 
     
     
       11. A method for a laser-induced plasma filament (LIPF) for an antenna element comprising the steps of:
 using a laser to generate a LIPF within an optically-transparent medium, wherein the laser is configured with an energy of at least 100 mJ and a pulse duration no longer than 20 ns; and 
 positioning the LIPF with respect to an existing metallic antenna, wherein the LIPF has a length that is longer than the existing metallic antenna such that the LIPF functions as a reflector for the existing metallic antenna thereby altering the existing metallic antenna's directivity. 
 
     
     
       12. The method of  claim 11 , further comprising generating a plurality of LIPF directors that are parallel to, and shorter in length than, the existing metallic antenna and are positioned on an opposite side of the existing metallic antenna from the reflector such that the LIFP directors absorb and reradiate radio waves from the existing metallic antenna with a different phase, modifying the existing metallic antenna's radiation pattern.